(postfix) SPAM filter?

Sten Daniel Soersdal wrote:
> We have a need for a relatively painless anti-spam solution that would
> reduce the amount of incoming spam (via postfix mail router). The
> problem is that i have little knowledge on what this actually means.
> Googling reveals a whole "universe" of interesting ways but what should
> i pursue?
> The things that are important to me is:
>> * Once it is setup then it would require no additional maintenance.
> * Potential spam messages are marked with a special header that can be
> filtered on user discretion on their local mail client software.
>> Neither performance, scalability, license nor cost is of much importance
> to me at this point.
>> Any hints?
No additional maintenance (less user add/delete)?:
http://www.postini.com
Unfortunately, it's been years since I've used their services so I can't
remember if they have the ability to mark and pass.
It's a hands-off solution that works.
Steve